This invention relates to a method of call processing at a communication node. More particularly, the invention relates to a method of call processing at a communication node in which, when the bandwidth of a path (line) between communication nodes undergoes upstream and downstream management separately and a call connection request that includes upstream/downstream reported bandwidths is issued, makes it possible to accept the call upon making the path for upstream communication and that for downstream communication different from each other.
In multimedia communications, there are many cases where communication speeds in the upstream and downstream directions differ, or in other words, where the necessary bandwidths in the upstream and downstream directions differ. In such cases, the conventional practice is to reserve the same bandwidth for the upstream and downstream directions on one path, as in the manner of telephone communications. That is, by reserving the bandwidth for whichever of the upstream or downstream direction requires the larger bandwidth, the bandwidths in both the upstream and downstream directions are assured. With this method, however, bandwidth that is not actually used also is reserved as necessary bandwidth. As a consequence, there is a decline in the efficiency with which the trunk circuit connecting communication nodes is used. Economy is sacrificed as a result.
Accordingly, a technique has been proposed (see the specification of Japanese Patent Application Laid-Open No. 61-56542) in which a connection request only in the upstream direction or a connection request only in the downstream direction is handled independently, thereby eliminating waste of upstream/downstream line bandwidth so that bandwidth will be utilized effectively. However, such prior art cannot deal with a call connection request that includes reported bandwidths in both the upstream and downstream directions. As a consequence, this technique cannot be applied to call admission control in which a call connection request includes reported bandwidths in both the upstream and downstream directions, as is the case in an ATM (Asynchronous Transfer Mode) network.
Accordingly, consideration has been given to a method that includes (1) managing the bandwidth of each path (line) separately in upstream and downstream directions; (2) when a call connection request that includes upstream/downstream reported bandwidths is issued, obtaining paths (lines) that satisfy respective ones of the reported bandwidths; (3) reserving bandwidth for each direction in each reported bandwidth; and (4) performing upstream and downstream communication via the paths obtained.
FIG. 32 is a schematic view showing the configuration of a communication system for implementing such method. Numeral 1 denotes an ATM exchange on the calling side, 2 an ATM exchange on the called side, 3 and 4 terminals, and 5 and 6 trunk circuits (paths) connecting the ATM exchanges. The ATM exchange 1 includes a call controller 1a for performing call control; a path-selection information storage unit 1b for storing upstream available bandwidth, downstream available bandwidth and line status of each path; an outgoing-path management unit 1c for referring to the path-selection information to determine whether a path satisfies upstream/downstream reported bandwidths; and a failure management unit 1d for detecting line (path) failure and notifying the call controller. The ATM exchange 2 also has a structure identical with that of the ATM exchange 1 and only a call controller 2a is illustrated.
The call controller 1a decides the outgoing path by a path selection protocol PNNI in response to a dynamic call connection request of an SVC (Switched Virtual Connection) or SPVC (Soft Permanent Virtual Connection), etc. The call controller 1a then queries the outgoing-path management unit 1c as to whether the upstream/downstream available bandwidths of the decided outgoing path are equal to or greater than the respective upstream/downstream reported bandwidths in the call connection request. The outgoing-path management unit 1c refers to the call selection information, determines whether the upstream/downstream available bandwidths of the outgoing path are equal to or greater than the respective upstream/downstream reported bandwidths in the call connection request and notifies the call controller 1a of the result. If the upstream/downstream available bandwidths of the outgoing path are both equal to or greater than the upstream/downstream reported bandwidths, the call controller 1a accepts the call connection request and transmits a call-connection request message (setup message) to the ATM exchange on the called side. Further, the outgoing-path management unit 1c updates the upstream/downstream available bandwidths of the above-mentioned path in the path-selection information storage unit 1b. On the other hand, if either of the available bandwidths is less than the reported bandwidth, the call controller 1a refuses call admission and does not transmit the call-connection request message to the ATM exchange on the called side. In other words, the call-connection request message is not transmitted unless the bandwidths in both directions are satisfied on the same line, even if there is available bandwidth that satisfies either the upstream bandwidth or downstream bandwidth of the connection (SVC or SPVC).
FIG. 33 is a diagram useful in describing the call admission operation. In a case where the upstream/downstream maximum bandwidth is 156 Mbps (written simply as 156M below), (1) indicates that 100M/100M are used in communication between terminals 31, 41 as the upstream/downstream bandwidths of a path 5 and that the upstream/downstream available bandwidths are 56M/56M, and (2) indicates that 110M/50M are used in communication between terminals 33, 43 as the upstream/downstream bandwidths of a path 6 and that the upstream/downstream available bandwidths are 46M/106M. If a call connection request in which the upstream/downstream reported bandwidths are 50M/80M, respectively, is issued between terminals 32 and 42 under these conditions, the upstream available bandwidth of 56M in case of path 5 will be greater than the upstream reported bandwidth of 50M but the downstream available bandwidth of 56M will be less than the downstream reported bandwidth of 80M. Further, the downstream available bandwidth of 106M in case of path 6 will be greater than the downstream reported bandwidth of 80M but the upstream available bandwidth of 46M will be less than the upstream reported bandwidth of 50M. As a consequence, the call connection request of upstream/downstream reported bandwidths 50M/80M is refused.
An arrangement in which the upstream/downstream reported bandwidths are allocated to separate paths on a per-single-direction basis when a call connection request is issued does not exist in the prior art. Consequently, there will be many cases where a path that satisfies both the upstream/downstream bandwidths does not exist. The end result is that it is necessary to add on physical lines per se. Further, in the cases mentioned above, much wasted available bandwidth that cannot be utilized in a trunk circuit is produced.